1. Field of the Invention
The present invention relates to a liquid crystal display device and methods of manufacturing the same in which a plurality of sub picture element electrodes are formed, which are made of a transparent conductive material such as indium tin oxide (ITO) and the like, the sub picture element electrodes are electrically connected to each other with connection wiring of narrow width.
2. Description of the Prior Art
Liquid crystal display devices have the advantages that they are thin and light and that they can be operative at low voltages and have low power consumption. Accordingly, liquid crystal display devices are widely used in various kinds of electronic devices. In particular, active matrix liquid crystal display devices in which a thin film transistor (TFT) is provided as a switching element for each picture element show excellent display quality which is comparable to that of cathode-ray tube (CRT) displays, and therefore have come to be widely used for displays for televisions, personal computers (PCs), and the like.
In general, a liquid crystal display device has a structure in which liquid crystals are sealed between two substrates, the substrates being disposed to face each other. On one substrate, a TFT, a picture element electrode, and the like are formed, while color filters, a common electrode, and the like are formed on the other substrate. Hereinafter, a substrate on which a TFT, a picture element electrode, and the like are formed is referred to as a TFT substrate; and a substrate, which is disposed to face the TFT substrate, is referred to as an opposite substrate. A structure formed by sealing liquid crystals between the TFT substrate and the opposite substrate is referred to as a liquid crystal panel.
FIG. 1 is a plan view showing one example of the conventional liquid crystal display device. FIG. 1 also shows a region for one picture element of a TFT substrate. Numeral 25 in FIG. 1 shows protrusions for alignment control provided on an opposite substrate.
As shown in FIG. 1, on the TFT substrate, a plurality of gate bus lines 11 extending in the horizontal direction (in the direction of X-axis) and a plurality of data bus lines 14 extending in the vertical direction (in the direction of Y-axis) are formed. Rectangular regions, which are sectioned by the gate bus lines 11 and the data bus lines 14, are picture elements regions, respectively.
On the TFT substrate, an auxiliary capacitance bus line 12 is placed in parallel with the gate bus lines 11, and formed across the center of a picture element region. The gate bus lines 11 and the auxiliary capacitance bus line 12 are covered with a first insulating film (gate insulating film), and the data bus lines 14 are formed on the first insulating film.
Furthermore, on the TFT substrate, a TFT 15, an auxiliary capacitance electrode 16, and a picture element electrode 18 are formed for each picture element region. In a liquid crystal display device shown in FIG. 1, the picture element electrode 18 is subdivided with slits 20 into three sub picture element electrodes 18a to 18c each being almost rectangular, and the sub picture element electrodes 18a to 18c are electrically connected to each other with connection wiring 19.
For the TFT 15, part of the gate bus lines 11 serves as a gate electrode, and a semiconductor film (not shown) formed on a predetermined region of the first insulating film serves as an active layer. A drain electrode 15a and a source electrode 15b of the TFT 15 are placed to face each other with a gate bus line 11 interposed therebetween, and are respectively connected to the semiconductor film. The drain electrode 15a is connected to the data bus lines 14, and the source electrode 15b is electrically connected to the sub picture element electrode 18a through a line 15c, as described later.
The auxiliary capacitance electrode 16 is placed to face the auxiliary capacitance bus line 12 with the first insulating film interposed therebetween. An auxiliary capacitance includes the auxiliary capacitance electrode 16, the auxiliary capacitance bus line 12, and the first insulating film interposed therebetween.
A second insulating film is formed on the gate bus lines 14, the TFT 15, and the auxiliary capacitance electrode 16; and, on this second insulating film, the three sub picture element electrodes 18a to 18c as described above are placed side by side in the direction of Y-axis. These sub picture element electrodes 18a to 18c are formed using a transparent conductive material such as indium tin oxide (ITO), and are electrically connected to each other with the connection wiring 19 made of a transparent conductive material of the same kind as above. The sub picture element electrode 18a is electrically connected to wiring 15c extending from the source electrode 15b through a contact hole 17a formed on the second insulating film. The sub picture element electrode 18b is electrically connected to the auxiliary capacitance electrode 16 through a contact hole 17b formed on the second insulating film.
On the opposite substrate, a common electrode, a color filter, and protrusions 25 for alignment control are provided. The common electrode is formed using a transparent conductive material such as ITO, and placed to face the sub picture element electrodes 18a to 18c on the TFT substrate. Color filters of three different colors, red (R), green (G), and blue (B), are prepared. A color filter of any one color among red, green, and blue is placed in each picture element. The protrusions 25 for alignment control are formed almost in cone using a dielectric material such as resin, and placed at positions facing to almost the centers of the sub picture element electrodes 18a to 18c. 
The TFT substrate and the opposite substrate are placed with spacers (not shown) interposed therebetween, and liquid crystals with negative dielectric anisotropy are sealed between these TFT and opposite substrates whereby a liquid crystal panel is formed. On both sides of the liquid crystal panel, polarizing plates are respectively disposed, and, further, a backlight is disposed on the backside (the opposite side of a face for observation) of the liquid crystal panel whereby a liquid crystal display device is constituted.
In the liquid crystal display device constituted in the above described way, the gate bus lines 11 are provided with scanning signals which cause the TFT 15 to be performed in on/off operation, and the data bus lines 14 are provided with display signals. When a voltage is not applied on a layer of liquid crystals, liquid crystal molecules are aligned almost perpendicular to the substrate surfaces. However, liquid crystal molecules in the vicinities of the protrusions 25 are aligned in directions perpendicular to the inclined surfaces of the protrusions 25. In this state, since light emitted from the backlight is blocked by two polarizing plates, a black display is presented.
When the scanning signals provided to the gate bus lines 11 cause the TFT 15 to be turned on, the sub picture element electrodes 18a to 18c are provided with the display signals, and liquid crystal molecules are inclined at angles in accordance with the voltages of the display signals. In this case, directions in which the liquid crystal molecules fall are determined by the protrusions 25 for alignment control and the lines of electric forces generated in oblique directions from edges of the sub picture element electrodes 18a to 18c to the outside; and the liquid crystal molecules are aligned in radial direction with respect to the protrusions 25 as centers. In this state, of the light emitted from the backlight, certain amount of light in accordance with inclined angles of the liquid crystal molecules is transmitted through the two polarizing plates, and emitted to the front side (observer side).
When the alignment directions of liquid crystal molecules in one picture element are uniform, display quality when viewed from an oblique direction is significantly deteriorated compared with that when viewed from the front. However, in the liquid crystal display device shown in FIG. 1, since the liquid crystal molecules as described above are aligned in radial direction with respect to the protrusions 25 as centers, the liquid crystal display device has the advantages that the display quality when viewed from an oblique direction is improved, and favorable viewing angle characteristics can be achieved.
FIG. 2 is a plan view showing another example of a conventional liquid crystal display device. FIG. 2 also shows a region for one picture element of a TFT substrate. Numerals 45 in FIG. 2 show protrusions for alignment control provided on an opposite substrate.
In this liquid crystal display device as in the foregoing described one, on the TFT substrate, gate bus lines 31 extending in the horizontal direction (in the direction of X-axis), data bus lines 34 extending in the vertical direction (in the direction of Y-axis), and an auxiliary capacitance bus line 32 which is placed in parallel with the gate bus lines 31 and which intersects a picture element region, are formed. The gate bus lines 31 and the auxiliary capacitance bus line 32 are covered with a first insulating film (gate insulating film), and the data bus lines 34 are formed on the first insulating film.
For each picture element region, the TFT 35, the auxiliary capacitance electrode 36, and a picture element electrode 38 are formed. For the TFT 35, part of the gate bus lines 31 serves as a gate electrode; and a drain electrode 35a and a source electrode 35b are placed to face each other with a semiconductor film (not shown) the film being placed over the gate electrode and interposed between the drain and source electrodes 35a, 35b. 
The auxiliary capacitance electrode 36 is formed to face an auxiliary capacitance bus line 32 with the first insulating film interposed therebetween. An auxiliary capacitance includes the auxiliary capacitance electrode 36, the auxiliary capacitance bus line 32, and the first insulating film interposed therebetween.
A second insulating film is formed on the gate bus lines 34, the TFT 35, and the auxiliary capacitance electrode 36; and, on this second insulating film, a picture element electrode 38 is formed using a transparent conductive material such as ITO. The picture element electrode 38 is subdivided into six sub picture element electrodes 38a to 38f using a plurality of slits 40 which are symmetrically formed on the upper and lower sides of the auxiliary capacitance bus line 32 with respect to the centerline thereof as the line of symmetry and which extend into oblique directions. However, the sub picture element electrodes 38a to 38f are electrically connected to each other with connection wiring 39 made of a transparent conductive material such as ITO. The sub picture element electrode 38a is connected to the source electrode 35b of the TFT 35 through a contact hole 37a formed on the second insulating film. The sub picture element electrode 38d is electrically connected to the auxiliary capacitance electrode 36 through a contact hole 37b formed on the second insulating film.
On the opposite substrate, a common electrode, a color filter, and protrusions 45 for alignment control are provided. The common electrode is formed using a transparent conductive material such as ITO, and placed to face the sub picture element electrodes 38a to 38f on the TFT substrate. Color filters of three different colors, red (R), green (G), and blue (B), are prepared. A color filter of any one color among red, green, and blue is placed in each picture element. The protrusions 45 for alignment control are made of a dielectric material such as resin, and placed in regions between the slits 40 of the picture element electrode 38 in parallel therewith.
The TFT substrate and the opposite substrate are placed with spacers (not shown) interposed therebetween, and liquid crystals with negative dielectric anisotropy are sealed between these TFT and opposite substrates whereby a liquid crystal panel is formed. On both sides of the liquid crystal panel, polarizing plates are respectively disposed, and, further, a backlight is disposed on the back of the liquid crystal panel whereby a liquid crystal display device is constituted.
In the liquid crystal display device constituted in the above described way, when a voltage is not applied on a layer of liquid crystals, liquid crystal molecules are aligned almost perpendicular to the substrate surfaces. However, liquid crystal molecules in the vicinities of the protrusions 45 are aligned in directions perpendicular to the inclined surfaces of the protrusions 45. In this state, since light emitted from the backlight is blocked by two polarizing plates, a black display is presented.
When the scanning signals provided to the gate bus lines 31 cause the TFT 35 to be turned on, the sub picture element electrodes 38a to 38f are provided with the display signals, and liquid crystal molecules are inclined at angles in accordance with the display signals. In this case, directions in which the liquid crystal molecules fall are determined by the protrusions 45 and the slits 40, and the liquid crystal molecules are aligned in directions perpendicular to the protrusions 45 and the slits 40. That is, in this liquid crystal device, a plurality of regions (domain) are formed, in which directions where the liquid crystal molecules fall are different while setting the protrusions 45 and the slits 40 as boundaries. In this state, of the light emitted from the backlight, certain amount of light in accordance with inclined angles of the liquid crystal molecules is transmitted through the two polarizing plates, and emitted to the front side (observer side).
In the liquid crystal display device shown in FIG. 2, in one picture element, a plurality of regions in which directions where the liquid crystal molecules fall are different are formed, and thus favorable viewing angle characteristics can be achieved.
However, both liquid crystal display devices as described above have the following problems. In the liquid crystal display device shown in FIG. 1, the sub picture element electrode 18a and the sub picture element electrode 18b; and the sub picture element electrode 18b and the sub picture element electrode 18c are connected with the connection wiring 19 which is made of a transparent conductive material such as ITO and which is small in width. Accordingly, once the connection wiring 19 breaks, a voltage is not transmitted to other sub picture element electrodes, hence coming to defective. It is considered to make the connection wiring 19 wider to avoid break. However, in that case, turbulence in alignment of liquid crystal molecules will occur in the connection wiring 19, hence causing deterioration in display quality.
In the liquid crystal display device shown in FIG. 2, since the sub picture element electrodes 38a to 38f are respectively connected through a plurality of connection wirings 39, only one break in the connection wiring 39 does not cause defect. However, since a transparent conductive material such as ITO has a relatively high resistance, when one of the wirings 39 even breaks, a voltage being applied on liquid crystals partly decreases, hence causing deterioration in display quality.